The present invention relates generally to a receiver and a method for receiving a first usable frequency band and a second usable frequency band, in particular to a broadband Low-IF dual receiver.
In many fields of communication technology, for example in satellite-aided positioning, it is desirable to be able to receive several usable frequency bands simultaneously or at least alternately in time. Apart from this, it is desirable, in particular in portable devices, to realize a circuit structure that is as simple as possible and a low power consumption.
Dual receivers allow the simultaneous reception of two different bands by a single receiver, which saves power consumption and costs.
In positioning, it can, for example, be necessitated to receive two bands of a navigation system (e.g. an L1-band and an L2c-band of the GPS-satellite navigation system, or an L5-band and an L6-band of the Galileo satellite navigation system) simultaneously. Also, simultaneous reception of bands of different systems can be desirable.
In the currently used receivers for the above described applications, there are two different groups: very broadband receivers and relatively narrow band receivers or dual receivers, respectively. Both cases are high-precision receivers for high-end navigation and positioning systems.
In a first type of receivers, high-precision is obtained by a large bandwidth of the transmission method DSSS (direct-sequence spread spectrum), wherein the bandwidth is, for example, between 20 MHz and 70 MHz or even more. Processing such a high bandwidth is a large challenge for the receiver. In particular, filtering and its group run time change in the pass band, cutoff frequency of a variable gain amplifier (also referred to as VGA) and a sampling rate of an analog/digital converter (also referred to as ADC) are affected. Due to the high cutoff frequency, an anti-aliasing filter is passively implemented. Further, due to the high cutoff frequency, the variable gain amplifier and the analog/digital converter (ADC) consume comparatively much current.
In a second type of receivers, high accuracy is obtained by simultaneously receiving two bands. This method compensates, among other things, an ionospheric group run time change (a negative influence variable in navigation systems) by measuring two delays from two different carrier frequencies.